Pressure activated safety valves may be incorporated into medical devices such as peripherally inserted central catheters (PICCs), ports, dialysis catheters and tunneled central catheters which provide long term access to the vascular system. Pressure activated safety valves generally include a slitted, flexible disk extending across a lumen. The flexible disk is generally constructed so that, when subjected to a threshold fluid pressure, edges of the slit separate from one another to permit flow through the lumen. When the pressure applied to the disk drops below the threshold level, the slit reseals to prevent leakage from or to the vascular access device. It would be desirable at times to employ within these vascular access devices fluid pressures in excess of the pressures to which these known flexible membranes have been traditionally exposed to with hand injections (e.g., when flushing an obstructed lumen, administering high-flow rate fluids, etc.).